Osteogenesis imperfecta (OI) type I is the mildest form of inherited brittle bone disease. Fibroblasts from affected individuals produce about half the expected amount of structurally normal type I collagen as a result of decreased synthesis of proal, one of its constituent chains. PCR amplification of genomic DNA followed by single-stranded conformational polymorphism electrophoresis (SSCP) and denaturing gradient gel electrophoresis (DGGE) has been used to identify mutations in the COLlA1 gene of type I collagen in patients with mild Osteogenesis imperfecta. One individual was identified with a single nucleotide substitution which alters the 5' donor splice site. RT-PCR was done on this fragment so that cDNA can be cloned and sequenced to evaluate the effect of this mutation on splicing. In addition, a polymorphism has been detected in the region of intron 2 which has not been previously described. Characterization of this polymorphism is in progress. Future studies will involve analysis of the regulatory mechanisms of type I collagen and screening OI patients Ior mutations in the first intron of the COLlA1 gene, where regulatory elements have been previously identified. The effect of these mutations on gene expression will be studied in fibroblast and osseous cell lines.